The technique disclosed in the present specification relates to a protection device for preventing overpower from flowing through a load circuit and, more particularly, to a technique for implementing, with a simple structure, a coil or a resistor and a capacitator of a lowpass filter for cutting a high-frequency waveform in an insulating layer of a semiconductor substrate in which a protection element that is turned on upon reception of overpower is formed.
Protection devices are known that are connected between a power source and a load circuit and protect the load circuit from overpower. Among such protection devices are ones in which a protection element that is a Zener diode or a combination of a Zener diode and a thyristor is formed in a semiconductor substrate. For example, JP-A-2015-198190 discloses a semiconductor substrate in which a protection element that is a combination of a Zener diode and a thyristor is formed.
To accommodate an input (noise or a surge current voltage) that is higher in frequency than a response band of a protection element, it is desirable to provide, in addition to the protection element, a lowpass filter including at least one of a coil, a resistor, and a capacitor between the input and output of a protection device. However, a protection device is made large in size if the protection device has such a lowpass filter separately from a semiconductor substrate.